There's nothing wrong with NSA sex but there's no reason to choose cheaters for it. If they're willing to lie to their wives, what makes you think they won't lie to you, maybe about important stuff that could affect your safety? Swingers clubs and Okcupid seem to be two good places to find married men in open marriages who are honest with their wives, just like you've been honest with your husband. In the former scenario you can meet the wife in person to confirm that she's ok with what's going on, in the latter you can chat with her online.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.